A capacitor is a basic electrical component of semiconductor devices such as semiconductor memory devices. A semiconductor memory device generally comprises a plurality of memory cells which are used to store a large quantity of information. Each memory cell includes a capacitor for storing electric charge and a corresponding field effect transistor for opening and closing charge and discharging passages of the capacitor. As the size of semiconductor devices continues to shrink, there is a desire to decrease the area occupied by each component of a semiconductor device. Capacitors are one component that can occupy considerable area on a semiconductor die depending on the size of the capacitor and/or the number of capacitors on the die.
One example of capacitors is a metal-insulator-metal (MIM) capacitor. MIM capacitors are typically made by forming a first metal plate on a substrate, forming a layer of dielectric material over the first metal plate and then forming a second metal plate over the layer of dielectric material. A traditional MIM capacitor is two-dimensional (2D), i.e., the two facing metal plates are planar and substantially parallel to each other and to the substrate. The capacitance of a MIM capacitor is a function of the surface area of the two facing metal plates and other parameters such as the dielectric constant of the dielectric material and the spacing between the two plates. Thus, one primary means to increase the capacitance of a MIM capacitor is to increase the sizes of the metal plates. However, this will consume more surface area of the substrate. Accordingly, a need exists to reduce the surface area on the substrate occupied by a capacitor without sacrificing its capacitance.
In addition, a capacitor is required to operate at high voltages for some applications, such as a decoupling capacitor in power amplifiers and microelectromechanical systems (MEMS). The reliability of a traditional capacitor will be significantly reduced under high operating voltages. Accordingly, there is a need to fabricate a capacitor with improved reliability as well.